How to determine the Shading Editor nodes that use a certain texture?
Just a short overview


List of all images is in Outliner > Blender file > Images
List of unused images is in Outliner > Orphan Data > Images
To delete selected items Right Click > Delete
To remove all orphaned data at once (except those with Fake user) use the nice Purge button


(Blender also 'Purges' all unused and unprotected images when you close it.)

There are three images in my file. Image 02 isn't used in any material so I can get rid of it.